This invention relates to an apparatus for assisting directional drilling in a well bore. More specifically, this invention relates to a drillable whipstock with an offset mandrel through which an anchoring means for the whipstock can be actuated.
During the drilling of a well for the production of the well and/or gas, it is often desirable to drill a directional hole, or well bore, through the side of the original well bore. Such sidetracking operations are performed for several reasons, such as avoiding, or drilling around drilling equipment which has become stuck in the original well bore. In addition, such operations make it possible to drill several wells from the original well bore. In such cases, it is often desirable to re-open the original well bore for the production of oil and gas therethrough.
Many sidetracking operations involve setting a cementitious kickoff plug of approximately 50-500 feet in length at the location to be sidetracked. Sidetrack plugs are typically set by lowering an open ended tubing string into the well bore and pumping a cementitious fluid through the tubing string and out the open end. Pressure in the well bore forces the cementitious fluid up the annulus between the tubing string and the well bore. The cementitious fluid is displaced until a sidetrack or kickoff plug of a desired length is set. The sidetracking operation then generally comprises using a bent sub to drill into the sidetrack plug and into side of the well bore. When such an operation is performed in an open, as opposed to a cased hole, directional drilling does not always successfully penetrate the side of the well bore. Such failures are partially due to the fact that the integrity of the cement is comprised during the setting of the plug due to mud contamination. Various other mechanical reasons can cause difficulty in penetrating the side of the well bore.
Other directional drilling techniques include setting a whipstock in a well bore. A whipstock has an inclined upper face, or ramp, which directs a drill bit into the side of the original well bore. A prior art method for setting a whipstock in a well bore is described in U.S. Pat. No. 5,287,921 to Blount et al. Typically, whipstocks are comprised of a non-drillable material such as steel. Therefore, to re-open the original well bore, the whipstock must be removed.
The present invention solves these problems by providing a whipstock which can be used in an open or a cased well bore, and which is comprised of a drillable material so that the well bore can be re-opened after sidetrack drilling operations have commenced.